This invention relates to methods of building bone in humans and other animals, i.e., for the treatment of osteoporosis and related disorders. In particular, this invention relates to such methods of treatment by administration of certain calcium salts.
Calcium is the fifth most abundant element in the human body. It plays an important role in many physiological processes, including nerve and muscle functions. Not surprisingly, nutritional and metabolic deficiencies of calcium can have broad-ranging adverse effects. Since about 90% of the body's calcium is found in bone tissues, many of these adverse effects are manifested through deficiencies in the structure, function and integrity of the skeletal system.
The most common metabolic bone disorder is osteoporosis. Osteoporosis can be generally defined as the reduction in the quantity of bone, or the atrophy of skeletal tissue. In general, there are two types of osteoporosis: primary and secondary. "Secondary osteoporosis" is the result of an identifiable disease process or agent. However, approximately 90% of all osteoporosis cases is idiopathic "primary osteoporosis". Such primary osteoporosis includes postmenopausal osteoporosis, age-associated osteoporosis (affecting a majority of individuals over the age of 70 to 80), and idiopathic osteoporosis affecting middle-aged and younger men and women.
For some osteoporotic individuals the loss of bone tissue is sufficiently great so as to cause mechanical failure of the bone structure. Bone fractures often occur, for example, in the wrist and spine of women suffering from postmenopausal osteoporosis. Kyphosis (abnormally increased curvature of the thoracic spine) may also result.
The mechanism of bone loss in osteoporotics is believed to involve an imbalance in the process of "bone remodeling". Bone remodeling occurs throughout life, renewing the skeleton and maintaining the strength of bone. This remodeling occurs in a series of discrete pockets of activity in the bone, called "osteoclasts" and "osteoblasts". Osteoclasts (bone dissolving or resorbing cells) are responsible for the resorption of a portion of bone within the bone matrix, during the resorption process. After resorption, the osteoclasts are followed by the appearance of osteoblasts (bone forming cells), which then refill the resorbed portion with new bone.
In a healthy adult, the rate at which the osteoclasts and osteoblasts are formed maintains a balance of bone resorption and bone formation. However, in osteoporotics an imbalance in this remodeling process develops, resulting in loss of bone at a rate faster than the accretion of bone. This imbalance is much more severe, and occurs at a younger age, in osteoporotics as compared to healthy adults.
Many compositions and methods are described in the medical literature for the "treatment" of osteoporosis. Many of these compositions and methods attempt to either slow the loss of bone or to produce a net gain in bone mass. See, for example, R. C. Haynes, Jr. et al., "Agents affecting Calcification", The Pharmacological Basis of Therapeutics, 7th Edition (A. G. Gilman, L. S. Goodman et al., Editors, 1985); and G. D. Whedon et al., "An Analysis of Current Concepts and Research Interest in Osteoporosis", Current Advances in Skeletogenesis (A. Ornoy et al., Editors, 1985). Estrogen is often used to affect the metabolism of calcium. Treatments using fluoride have also been described. However, the utility of such agents may be limited, due to possible adverse side effects. See W. A. Peck, et al., Physician's Resource Manual on Osteoporosis (1987), published by the National Osteoporosis Foundation (incorporated by reference herein).
Nutritional therapies for osteoporosis have also been proposed. Many calcium-containing compounds and compositions have been described for use as nutritional supplements. Many commercial preparations are also available, typically containing calcium carbonate. Calcium chloride, calcium gluceptate, calcium gluconate, calcium lactate, calcium phosphate, calcium citrate, and other calcium salts have also been described for use in calcium supplements. The use of calcium citrate, for example, is described in French Patent 2,219,778, Monteau, published Sep. 27, 1974; and World Patent Publications 86/04814 and 86/04815, Pak et al., both published Aug. 28, 1986. Food supplements containing calcium citrate malate are described in Japanese Patent Document 56/97, 248, Kawai, published Aug. 5, 1981.
The utility of these known supplements varies. Unlike agents (such as estrogen) which affect the metabolism of bone, calcium nutritional supplements have been thought to merely provide a source for calcium (which may or may not be properly absorbed and metabolized). Indeed, the literature is bereft of any credible clinical data supporting the utility of any of these calcium supplements to actually treat osteoporosis (to actually build bone). See, for example, B. Riis et al., "Does Calcium Supplementation Prevent Postmenopausal Bone Loss?", 316 New England J. of Medicine 173-177 (1987); L. Nilas et al., "Calcium Supplementation and Postmenopausal Bone Loss", 289 British Medical Journal 1103-1106 (1984); and H. Spencer et al., "NIH Consensus Conference: Osteoporosis", 116 Journal of Nutrition 316-319 (1986).
It has now been discovered, however, that certain methods of treatment, involving the administration of mixtures of certain calcium salts, are surprisingly effective for the building of bone. In particular, as compared to nutritional regimens known in the art, these methods afford greater efficacy in the treatment of osteoporosis and related disorders.